Mixing Regimes in a Shallow Lake over the Past Five Decades: Application to Laguna Carén

This study presents a 50-year hydrodynamic simulation of Laguna Carén, a shallow lake near the capital of Chile, utilizing the 3-Dimensional coupled Hydrodynamic-Aquatic Ecosystem Model, AEM3D, to investigate the factors influencing the mixing regimes of the water column. The model incorporates key processes, such as heat and momentum exchanges with the atmosphere, light penetration, and heat diffusion in sediments, all fundamental for understanding the hydrodynamics of the lake. The obtained results allowed classifying the mixing regime of the lake in rarely mixed (RM), intermittently mixed (IM), and often-mixed (RM) regimes. Furthermore, the numerical results reveal a significant differentiation between IM and OM years, primarily driven by changes in meteorological forces, particularly wind speed. The analysis indicates that increased wind speeds enhance turbulent kinetic energy, leading to a reduction in the percentage of time the water column is stratified, whereas lower wind conditions promote stable stratification. This study shows that the mixing regime in shallow lakes can exhibit dramatic changes in response to minor alterations in meteorological conditions, particularly wind speed. Such changes in mixing regimes may result in unpredictable consequences for the ecology of the lake.